the expression of eukaryotic genes is very different than what we have learned from prokaryotic studies. One of the most intriguing phenomenon is the fact that many, but not all, eukaryotic genes have their mature structural coding sequences disrupted by intervening sequences which must be spliced out during messenger processing. the studies proposed focus on elucidating the specific uncleic acid structural and sequence features required for messenger RNA splicing. In pursuit of these goals, a combination of synthetic and recombinant DNA technology will be utilized to create gene fusions which will facilitate the study of messenger splicing requirements in the lower eukaryote Saccharomyces cerevisiae. this system is a desirable experimental system for these studies for a variety of reasons, the most salient of which are: it is known to have messenger splicing activity, it is genetically well defined, and easily manipulable with respect to recombinant DNA technology. In addition to the investigation of nucleic acid sequence and structural requirements, the proposed research will explore the role of small nuclear ribonucleoprotein particles (snRNPs) in messenger splicing. Synthetic DNA will be utilized as a probe for following the purification of a specific class of these particles and as well as an affinity ligand in the purification scheme. The long range goal of the proposed research is to develop an indepth understanding of the factors governing the regulation of this important biological process. Such an understanding will provide the basis for treatment of genetic and biochemical abnormalities which alter the normal splicing pathways.